Notebook PCs and tablet PCs (hereinafter, referred to as tablets) are widely used. These apparatuses are equipped with wireless communication devices for accessing the Internet in mobile environments. It is known that radio waves may cause heating effects on human bodies if their levels are high. Since a strength of radio waves which causes the effects on the human bodies has been found out, safety standards of radio waves are established on the basis of the strength. Wireless output of the apparatuses must satisfy the safety standards.
Therefore, the apparatuses each include a proximity sensor which detects the approach of a human body, and is configured to control transmission output when being approached by the human body. The proximity sensor is, for example, a capacitive detection sensor. A capacitor is formed of two parallel plates in which a detection surface of the sensor is one electrode and an object to be detected (human body) is the other electrode, and the proximity of the object to be detected can be detected on the basis of capacitance between the electrodes.
In recent years, detachable PCs have been developed. A detachable PC corresponds to a normal notebook PC in which a display and a keyboard (also referred to as a keyboard dock) are attachable and detachable. The display can be used alone as a tablet. When the display is fixed to a docking port of the keyboard dock, the detachable PC assumes the form of an open notebook PC, and can be used as if it were a notebook PC. In the form of a notebook PC, the docking port can be rotated by a hinge mechanism, and the display can be closed while being fixed to the keyboard dock. In this case, a display screen of a tablet 10 faces the keyboard dock 12 and is not exposed. If the display can be fixed to the docking port either face up or face down, the detachable PC can also be used as if it were a tablet, by closing the display while fixing the display to the docking port of the keyboard dock 12 in a reverse way to that in the form of a notebook PC to make a back surface of the tablet 10 face the keyboard dock 12 and expose the display screen. Since the tablet 10 is laid on the keyboard dock 12, a proximity sensor may detect the proximity of the keyboard dock 12, not the human body and unnecessarily decrease transmission output although not being approached by the human body, whereby wireless communication performance deteriorates.